RELATIVE ABUNDANCE AND ROLE OF BRACONID LARVAL PARASITOIDS IN CONTAINING LEPIDOPTERAN POPULATIONS IN DISTRICT FAISALABAD

Abstract

Conservation involves sustaining of biological diversity as its main goal. Description of all taxa and their relative abundance are the most important components of biodiversity conservation within an ecosystem. Lepidoptera is one of the largest orders of the class Insecta. They are phytophagous as well as pollinators. Parasitoids are the biological control agents cosmopolitan in nature and keep check on caterpillars, by parasitizing them. Identifying and conserving these biological control agents is important as it allows us to rely less on chemicals, and hence reduce their impacts on ecosystems. The Braconidae (Hymenoptera: Ichneumonoidea) is among one of the largest families, being used successfully in biological control programs worldwide. The present study aimed at identifying the relative abundance of some of the braconids and their lepidopteran hosts from the cropland of district Faisalabad, Punjab, Pakistan. For this purpose, sampling was carried out from four crops, namely wheat, fodder, brassica and vegetables, for one year from June, 2010 to May, 2011. Fodder was the most infested crop, with 37.28% of the total lepidopteran specimens, followed by vegetables (36.25%), brassica (23.08%) and the least being wheat (3.38%). A similar trend was observed for braconids, being 31.90%, 25.38%, 21.63% and 21.08% for fodder, vegetables, brassica and wheat, respectively. Host-parasitoid associations, helpful in designing biological control programs, were assessed by regression analysis. Pieris brassicae showed the best probable association with Heterospilus spp., Cotesia flavipes and Cotesia vestalis, having R 2 values as 0.96, 0.95 and 0.94, respectively. Quantification of foraging of lepidopteran caterpillars was done to understand suitability of different host plants for cultural control measures. P. brassicae was found to be the most destructive species, with maximum larval duration of 17.67±0.47 days on brassica plants, followed by Helicoverpa armigera 17.00±0.82 days on cauliflower. Trichoplusia ni had maximum larval duration of 14.3±0.47 days on cabbage, and those of Spodoptera exigua had 14.00±0.47 days on cauliflower. The average consumption of all food offered by larvae of P. brassicae, H. armigera, T. ni and S. exigua was calculated as 14.67±5.75g, 11.76±5.25g, 10.75±5.25g and 8.99±6.15g respectively. Brassica was the preferred crop for P. brassicae, as maximum larval length (36.45±0.05mm), pupal length (20.00±0.82mm) and adult length (43.00±0.81mm) was observed when larvae fed on this crop. Cauliflower was the preferred diet for S. exigua and H. armigera. Both of the species showed maximum size of larvae (35.4±0.00mm, and 47.00±0.00mm), pupae (18.33±0.47mm and 19.67±0.47mm) and adults (26.00±0.47mm and 35±0.81mm), respectively, when fed on cauliflower. P. brassicae was found to be a potential host for two species of the genus Cotesia, namely C. vestalis and C. flavipes. In the present study Sequence Characterized Amplified Regions (SCARs) could only be developed for species identification of T. ni due to experimental and financial limits. Such types of studies are very helpful in designing biological control programs for assessment and control of economic pests.